The 1010a IAQ meter uses state of the art sensors to measure humidity, carbon monoxide (CO), carbon dioxide (CO2), and temperature. The CO and CO2 sensors in your meter will need to be replaced periodically and calibration is recommended once every year. The CO sensor is electrochemical and this type of sensor is always active once installed in the unit. Therefore the time the unit is off and not being used must be taken into account when determining sensor life. The sensors in your analyzer are warranted for two years.